The water relations of hemlock (Tsuga canadensis). III. The temperature dependence of water exchange in a pressure bomb

1973 ◽  
Vol 51 (8) ◽  
pp. 1537-1543 ◽  
Author(s):  
M. T. Tyree ◽  
M. Benis ◽  
J. Dainty
Keyword(s):  
Activation Energy ◽  
Temperature Dependence ◽  
Water Exchange ◽  
Membrane Resistance ◽  
Tsuga Canadensis ◽  
Rate Equations ◽  
Rate Theory ◽  
Water Permeation ◽  
Pressure Bomb ◽  
Extracellular Resistance

The pressure-bomb technique has been used to measure the temperature dependence of water exchange between the apoplast and symplast of hemlock (Tsuga canadensis) shoots. By applying the Arrhenius rate theory, the activation energy for water exchange in the whole shoot equals 25.9 + 0.6 × 103 J per mole. A theory is proposed on the basis of the Arrhenius rate equations which allows us to predict the relative magnitudes of the membrane resistance, Rm, and the extracellular resistance, Rx, to water permeation. On the basis of our calculations, we believe Rm is at least one-quarter of Rx and may even exceed Rx, but more work needs to be done to be sure.

The water relations of hemlock (Tsuga canadensis). IV. The dependence of the balance pressure on temperature as measured by the pressure-bomb technique

1974 ◽  
Vol 52 (5) ◽  
pp. 973-978 ◽  
Author(s):  
M. T. Tyree ◽  
J. Dainty ◽  
D. M. Hunter
Keyword(s):  
Temperature Dependence ◽  
Water Potential ◽  
Osmotic Pressure ◽  
Water Relations ◽  
Turgor Pressure ◽  
Tsuga Canadensis ◽  
Constant Volume ◽  
Pressure Bomb

The temperature dependence of the balance pressure is reported for shoots of Tsuga canadensis at constant volume, i.e., when water is neither added to nor removed from the shoot. Since the balance pressure closely equals minus the water potential, the temperature dependence of the balance pressure should reflect the combined temperature dependence of the osmotic and turgor pressures. Both the osmotic and the turgor pressures decline with decreasing temperature; frequently the turgor pressure declines 2 to 3 times more rapidly than the osmotic pressure, causing the balance pressure to rise with decreasing temperature. Only when the turgor pressure is zero (only beyond incipient plasmolysis) does the temperature dependence of the balance pressure closely follow the temperature dependence of the osmotic pressure; this occurs when the balance pressure equals or exceeds 24 bars.

The water relations of hemlock (Tsuga canadensis). II. The kinetics of water exchange between the symplast and apoplast

1973 ◽  
Vol 51 (8) ◽  
pp. 1481-1489 ◽  
Author(s):  
M. T. Tyree ◽  
J. Dainty
Keyword(s):  
Water Exchange ◽  
Turgor Pressure ◽  
Experimental Studies ◽  
Tsuga Canadensis ◽  
Rate Of Change ◽  
Cell Constant ◽  
Exponential Process ◽  
Pressure Increment ◽  
Pressure Bomb ◽  
Kinetics Of

We present a theoretical analysis of the events that occur while a plant enclosed in a pressure bomb evolves from one equilibrium balancing pressure to another. The initial rate of efflux from any one cell in response to a pressure increment of ΔP equals (ALp)i ΔP, where (ALp)i is the surface area times hydraulic conductivity of the cell's semipermeable membrane(s). If the volume changes and pressure increment are small, the cell will approach equilibrium exponentially. The half time of the exponential process is governed by (ALp)iki, where ki is the cell constant (= the combined rate of change of osmotic and turgor pressure with the volume expressed from the cell). Experimental studies of the kinetics of water exchange between the symplast and apoplast of hemock (Tsuga canadensis) shoots in a pressure bomb reveal that the cells collectively behave as though they fall into three distinct populations which approach equilibrium with different half times.

The water relations of hemlock (Tsuga canadensis). V. The localization of resistances to bulk water flow

1975 ◽  
Vol 53 (10) ◽  
pp. 1078-1084 ◽  
Author(s):  
M. T. Tyree ◽  
C. Caldwell ◽  
J. Dainty
Keyword(s):  
Activation Energy ◽  
Water Flow ◽  
Water Exchange ◽  
Careful Analysis ◽  
Bulk Water ◽  
Exponential Process ◽  
Measurable Amount ◽  
Pressure Bomb ◽  
Overall Resistance ◽  
Kinetics Of

The pressure-bomb technique has been used to measure the kinetics of water exchange while a plant enclosed in a pressure bomb evolves from one equilibrium balance pressure to another. In earlier studies two observations were made. (1) The kinetics of water exchange appeared to be described by an exponential process in which three populations of cells exchange water with apoplast independently of each other. (2) The temperature dependence of the tempo of water exchange yielded an activation energy of 25.9 ± 0.6 × 103 J/mol, which is higher than the activation energy for laminar flow of water in pipes (= 17 × 103 J/mol). These results have been repeated and a more careful analysis has been conducted involving infiltration of air spaces in leaves with water and the selective removal of the leaves. It now appears that the xylem network up to (but not including) the leaves contributes about two thirds of the resistance to water flow in whole shoots 15 to 40 g in fresh weight. Presumably leaves near the cut basal end of the shoot experience a smaller xylem resistance than leaves near the apex. The kinetics of water exchange from water in the air spaces of infiltrated shoots indicates that there is a barrier at the air–water interface of leaves that equals the normal shoot resistance to bulk water flow. The activation energy for water flow through the xylem alone was measured to be about 17 × 103 J/mol. Although the leaves contribute a measurable amount to the overall resistance to water flow, the mathematical description of the system is much more complicated than previously supposed.

On the interpretation of dislocation-loop growth during in-situ high-voltage Electron Microscopy

1990 ◽  
Vol 48 (4) ◽  
pp. 532-533
Author(s):  
E. Holzäpfel ◽  
F. Phillipp ◽  
M. Wilkens
Keyword(s):  
Point Defect ◽  
Rate Equations ◽  
Rate Theory ◽  
Dislocation Loops ◽  
High Voltage Electron Microscopy ◽  
Vacancy Migration ◽  
Voltage Electron ◽  
Reaction Rate Theory ◽  
Defect Reactions

During in-situ radiation damage experiments aiming on the investigation of vacancy-migration properties interstitial-type dislocation loops are used as probes monitoring the development of the point defect concentrations. The temperature dependence of the loop-growth rate v is analyzed in terms of reaction-rate theory yielding information on the vacancy migration enthalpy. The relation between v and the point-defect production rate P provides a critical test of such a treatment since it is sensitive to the defect reactions which are dominant. If mutual recombination of vacancies and interstitials is the dominant reaction, vαP0.5 holds. If, however, annihilation of the defects at unsaturable sinks determines the concentrations, a linear relationship vαP is expected.Detailed studies in pure bcc-metals yielded vαPx with 0.7≾×≾1.0 showing that besides recombination of vacancies and interstitials annihilation at sinks plays an important role in the concentration development which has properly to be incorporated into the rate equations.

P+ implanted 6H-SiC n+-i-p diodes: evidence for a post-implantation-annealing dependent defect activation

2014 ◽  
Vol 1693 ◽  
Author(s):  
R. Nipoti ◽  
M. Puzzanghera ◽  
F. Moscatelli
Keyword(s):  
Activation Energy ◽  
Temperature Dependence ◽  
Ideality Factor ◽  
Low Voltage ◽  
Reverse Current ◽  
Forward Current ◽  
Current Region ◽  
Recombination Centers ◽  
Energy Dependent ◽  
Post Implantation

ABSTRACTTwo n+-i-p 6H-SiC diode families with P+ ion implanted emitter have been processed with all identical steps except the post implantation annealing: 1300°C/20min without C-cap has been compared with 1950°C/10min with C-cap. The analysis of the temperature dependence of the reverse current at low voltage (-100V) in the temperature range 27-290°C shows the dominance of a periphery current which is due to generation centers with number and activation energy dependent on the post implantation annealing process. The analysis of the temperature dependence of the forward current shows two ideality factor n region, one with n = 1.9/2 at low voltage and the other one with 1 < n < 2 without passing through 1 for increasing voltages. For both the diode families the current with n = 1.9/2 is a periphery current due to recombination centers with a thermal activation energy near the 6H-SiC mid gap. In the forward current region of 1 < n < 2, the two diode families show different ideality factor values which could be attributed to a different post implantation annealing defect activation.

Diffusion of Ce-Al Melts Measured by Sliding Cell Technique

2017 ◽  
Vol 898 ◽  
pp. 679-683
Author(s):  
Cheng Chen ◽  
Jin Liang Hu ◽  
Lang Xiang Zhong ◽  
Bo Zhang
Keyword(s):  
Activation Energy ◽  
Temperature Dependence ◽  
Strong Interaction ◽  
Al Alloy ◽  
Diffusion Behavior ◽  
Diffusion Constants

The diffusion behavior of Ce-Al alloy melt at three temperatures of 943K, 953K and 963K was investigated by sliding shear method. The inter-diffusion constants D show Arrhenius-type temperature dependence in the investigated regimes. Compared with the previous results achieved in Ce-Cu melt, liquid Ce-Al displays a much slower diffusion behavior and rather higher activation energy ED, which was caused by the strong interaction between Ce and Al.

scholarly journals SYNTHESIS AND ELECTRICAL CONDUCTIVITY OF SOLID SOLUTIONS OF THE SYSTEM RbF-PbF2-SnF2

2019 ◽  
Vol 85 (5) ◽  
pp. 60-68
Author(s):  
Yuliay Pogorenko ◽  
Anatoliy Omel’chuk ◽  
Roman Pshenichny ◽  
Anton Nagornyi
Keyword(s):  
Activation Energy ◽  
Electrical Conductivity ◽  
Temperature Dependence ◽  
Solid Solutions ◽  
Basic Structure ◽  
Elementary Cell ◽  
Initial Structure ◽  
Fluoride Ions ◽  
Temperature Range ◽  
Order Of Magnitude

In the system RbF–PbF2–SnF2 are formed solid solutions of the heterovalent substitution RbxPb0,86‑xSn1,14F4-x (0 < x ≤ 0,2) with structure of β–PbSnF4. At x > 0,2 on the X-ray diffractograms, in addition to the basic structure, additional peaks are recorded that do not correspond to the reflexes of the individual fluorides and can indicate the formation of a mixture of solid solutions of different composition. For single-phase solid solutions, the calculated parameters of the crystal lattice are satisfactorily described by the Vegard rule. The introduction of ions of Rb+ into the initial structure leads to an increase in the parameter a of the elementary cell from 5.967 for x = 0 to 5.970 for x = 0.20. The replacement of a part of leads ions to rubium ions an increase in electrical conductivity compared with β–PbSnF4 and Pb0.86Sn1.14F4. Insignificant substitution (up to 3.0 mol%) of ions Pb2+ at Rb+ at T<500 K per order of magnitude reduces the conductivity of the samples obtained, while the nature of its temperature dependence is similar to the temperature dependence of the conductivity of the sample β-PbSnF4. By replacing 5 mol. % of ions with Pb2+ on Rb+, the fluoride ion conductivity at T> 450 K is higher than the conductivity of the initial sample Pb0,86Sn1,14F4 and at temperatures below 450 K by an order of magnitude smaller. With further increase in the content of RbF the electrical conductivity of the samples increases throughout the temperature range, reaching the maximum values at x≥0.15 (σ573 = 0.34–0.41 S/cm, Ea = 0.16 eV and σ373 = (5.34–8.16)•10-2 S/cm, Ea = 0.48–0.51 eV, respectively). In the general case, the replacement of a part of the ions of Pb2+ with Rb+ to an increase in the electrical conductivity of the samples throughout the temperature range. The activation energy of conductivity with an increase in the content of RbF in the low-temperature region in the general case increases, and at temperatures above 400 K is inversely proportional decreasing. The nature of the dependence of the activation energy on the concentration of the heterovalent substituent and its value indicate that the conductivity of the samples obtained increases with an increase in the vacancies of fluoride ions in the structure of the solid solutions.

PHOTOELECTRIC PROPERTIES OF MnIn2S4 SINGLE CRYSTALS

2021 ◽  
Vol 88 (6) ◽  
pp. 967-969
Author(s):  
N. N. Niftiyev
Keyword(s):  
Activation Energy ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Spectral Distribution ◽  
Photoconductivity Spectrum ◽  
Intracenter Transition ◽  
Photoelectric Properties ◽  
Impurity Photoconductivity ◽  
Donor Defect

The spectral distribution of the photoconductivity and the temperature dependence of the photocurrent of MnIn2S4 single crystals are investigated. The intrinsic, impurity photoconductivity and a maximum at an energy of 2.69 eV, which is associated with the intracenter transition of Mn2+ ions (6A1→4A1), are revealed in the photoconductivity spectrum. The region of the wavelengths of 600–1000 nm appears with an excess of manganese in the crystals and is caused by a donor defect. At temperatures of 80—145 K, the increase in the photocurrent is associated with the thermal depletion of the adhesion levels. The activation energy of the adhesion levels is determined.

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